Imaging optical system and microscope system

ABSTRACT

An imaging optical system includes an objective, an image-formation optical system, and an image sensor, wherein an object, the objective, the image-formation optical system, and the image sensor are arranged in this order, the objective includes: a first lens group that includes a meniscus lens component that is the closest to an image among the first lens group, the meniscus lens component having a convex surface facing the object; and a second lens group that is closer to the image than the first lens group is, and the imaging optical system satisfies the following conditional expression: 
       4×10 6   ≤PX   n ≤1×10 10   (1)
         where PX n  indicates the number of pixels included in a region on the image sensor in which an MTF specific to an e line is 40% or higher at a spatial frequency of 750×NA i  [LP/mm], and NA i  indicates the numerical aperture of the image side of the imaging optical system.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2018-080954, filed Apr. 19, 2018,the entire contents of which are incorporated herein by this reference.

BACKGROUND OF THE INVENTION Field of the Invention

The disclosure herein relates to an imaging optical system and amicroscope system.

Description of the Related Art

In the field of microscopes, the use of observation and analysis ofmicroscopic images captured by a digital camera has been expanded inaddition to the use of visual observation using an eyepiece. A techniquehas also been used wherein a plurality of microscopic images having ahigh resolution are pieced together to construct a microscopic imagecorresponding to a wide region (hereinafter referred to as a virtualslide image).

Such a technique is described in, for example, Japanese Laid-open PatentPublication No. 2007-121837. The use of the technique described inJapanese Laid-open Patent Publication No. 2007-121837 has been expandedespecially in pathological diagnoses, in which a wide region needs to beobserved with a high resolving power without overlooking portions to bediagnosed.

SUMMARY OF THE INVENTION

An imaging optical system in accordance with an aspect of the presentinvention includes an objective, an image-formation optical system, andan image sensor, wherein an object, the objective, the image-formationoptical system, and the image sensor are arranged in this order. Theobjective includes: a first lens group that includes a meniscus lenscomponent that is the closest to an image among the lens components ofthe first lens group, the meniscus lens component having a convexsurface facing the object; and a second lens group that is closer to theimage than the first lens group is. The imaging optical system satisfiesthe following conditional expression:

4×10⁶ PX _(n)1×10¹⁰  (1)

In this conditional expression, PX_(n) indicates the number of pixelsincluded in a region on the imaging plane of the image sensor in whichan MTF specific to an e line is 40% or higher, the MTF specific to the eline is an MTF achieved at a spatial frequency of 750×NA_(i) [LP/mm],and NA_(i) indicates the numerical aperture of the image side of theimaging optical system.

A microscope system in accordance with an aspect of the presentinvention includes the imaging optical system in accordance with theabove-described aspect and an image construction unit that constructs avirtual slide image by piecing together a plurality of first imagescaptured by the imaging optical system. The microscope system satisfiesthe following conditional expression:

3.3×10⁶ ≤PX _(i)≤1×10¹⁰  (9)

where PX_(i) indicates the number of pixels that constitute eachindividual image of the plurality of first images.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more apparent from the following detaileddescription when the accompanying drawings are referenced.

FIG. 1 illustrates the configuration of a microscope system 100 inaccordance with an embodiment;

FIG. 2 is a cross-sectional view of an imaging optical system 10;

FIG. 3 is a cross-sectional view of an objective 1;

FIGS. 4A-4D are each an aberration diagram for an imaging optical system10;

FIG. 5 is a cross-sectional view of an imaging optical system 20;

FIG. 6 is a cross-sectional view of an objective 2;

FIGS. 7A-7D are each an aberration diagram for an imaging optical system20;

FIG. 8 is a cross-sectional view of an imaging optical system 30;

FIG. 9 is a cross-sectional view of an objective 3;

FIGS. 10A-10D are each an aberration diagram for an imaging opticalsystem 30;

FIG. 11 is a cross-sectional view of an imaging optical system 40;

FIG. 12 is a cross-sectional view of an objective 4;

FIGS. 13A-13D are each an aberration diagram for an imaging opticalsystem 40;

FIG. 14 is a cross-sectional view of an imaging optical system 50;

FIG. 15 is a cross-sectional view of an objective 5;

FIGS. 16A-16D are each an aberration diagram for an imaging opticalsystem 50;

FIG. 17 is a cross-sectional view of an imaging optical system 60;

FIG. 18 is a cross-sectional view of an objective 6; and

FIGS. 19A-19D are each an aberration diagram for an imaging opticalsystem 60.

DESCRIPTION OF THE EMBODIMENTS

In recent years, there has been an increasing need to capturehigh-resolution microscopic images for a wide field of view and quicklyconstruct a virtual slide image corresponding to a wide range with ahigh resolution by piecing these microscopic images together. Imagingoptical systems that can have a high resolving power for a wider fieldof view than those in the prior art are necessary to meet such a need.

The following describes embodiments of the present invention.

FIG. 1 illustrates the configuration of a microscope system 100 inaccordance with an embodiment. The microscope system 100 includes: amicroscope body provided with a digital camera 112; a computer 118; andinput-output apparatuses (display 119 a, keyboard 119 b, and mouse 119c) connected to the computer 118.

The microscope body is, for example, a fluorescence microscope andincludes an imaging optical system 110 that captures a microscopic imageof a sample S. The imaging optical system 110 includes an objective 101,an image-formation optical system 111, and a digital camera 112 providedwith an image sensor 112 a, wherein the sample S, the objective 101, theimage-formation optical system 111, and the digital camera 112 arearranged in this order. The microscope body further includes a stage 114on which the sample S is to be placed, a light source 115 a, a lightsource 115 b, a condenser 116, and an eyepiece 117.

The objective 101 is an infinity-corrected microscope objective to beused in combination with the image-formation optical system 111. Theimage-formation optical system 111 converges a pencil of infinitelydistant light rays emitted from the objective 101 and forms an opticalimage of the sample S on an imaging plane 112 s of the image sensor 112a.

The image-formation optical system 111 may be a common single tube lenshaving a focal length of about 180-200 mm. The image-formation opticalsystem 111 may be provided by coupling the tube lens to an adapteroptical system that enlarges or reduces an image formed by the tubelens.

The digital camera 112 includes an image sensor 112 a that convertsincident light into an electric signal. The digital camera 112 generatesimage data of a microscopic image by shooting an image of the sample Sand outputs the image data to the computer 118.

The stage 114 is, for example, a motorized stage. The stage 114 is notlimited to a motorized stage but may be a manual stage.

The light source 115 a is an epi-illumination light source. The lightsource 115 a is, for example, a lamp light source such as a mercuryvapor lamp or a xenon lamp. The light source 115 b is atransmitted-illumination light source and is attached to a rear portionof the microscope body. When the microscope body is a laser scanningmicroscope, the light sources 115 a and 115 b may each be a laser lightsource.

The condenser 116 includes a condensing lens for irradiating the sampleS with illumination light. A condenser to be placed on an optical pathmay be selected from a plurality of condensers mounted on a turretaccording to a microscopic method and/or an illumination range.

The eyepiece 117 is mounted in a trinocular lens barrel of themicroscope body.

The microscope body depicted in FIG. 1 is an upright microscope.However, the microscope body may be an inverted microscope. Themicroscope body is not limited to a fluorescence microscope and mayaccommodate any microscopies such as a bright-field observation method,a dark-field observation method, a differential-interface-contrastobservation method, and a phase-contrast observation method.

The computer 118 is, for example, a standard computer provided with aprocessor and a memory and communicably connected to the microscopebody. By the processor running a program stored in the memory, thecomputer 118 functions as an image construction unit that constructs avirtual slide image by piecing together a plurality of microscopicimages captured by the imaging optical system 110.

More particularly, the computer 118 changes the position of the sample Srelative to the objective 101 by controlling the stage 114. In addition,the computer 118 captures a microscopic image of the sample S for theposition after the change by controlling the digital camera 112. In thiscase, the stage 114 is controlled in a manner such that a field of viewbefore the change and a field of view after the change partially overlapeach other. This control process is repeated to capture a plurality ofmicroscopic images. The computer 118 then determines piecing positionsby performing an alignment process between the plurality of microscopicimages and finally pieces the plurality of microscopic images togetherat these piecing positions. Accordingly, a virtual slide image thatcorresponds to a wide range on the sample S is constructed.

The computer 118 may designate an imaging range for the digital camera112. In particular, the digital camera 112 may capture a microscopicimage using only pixels of the image sensor 112 a that are locatedwithin a region relatively close to an optical axis, i.e., a region forwhich aberrations are corrected in a preferable manner. This allowsmicroscopic images having a high image quality for a range from thecenter to edge portions to be obtained so that a high image quality canalso be achieved for the entirety of a virtual slide image constructedby piecing these microscopic images together.

The display 119 a is, for example, a liquid crystal display, an organiclight emitting display (OLED), a cathode ray tube (CRT) display. Thedisplay 119 a displays an image on the basis of an image signal inputfrom the computer 118.

The keyboard 119 b and the mouse 119 c, which are each an apparatus tobe directly used by a user of the microscope system 100, outputs anoperation signal that depends on user operations to the computer 118.

The microscope system 100 configured as described above is such that theimaging optical system 110 has a high resolving power for a wide fieldof view. Hence, a wide range can be imaged in a single image shootingoperation so as to capture a microscopic image having a high resolution,and only a small number of image shooting operations need to beperformed to construct a virtual slide image. Accordingly, ahigh-quality virtual slide image can be captured in a short time.

The following describes an imaging optical system 110 in accordance withan embodiment of the present application in detail.

As described above, the imaging optical system. 110 includes anobjective 101, an image-formation optical system 111, and an imagesensor 112 a, wherein an object, the objective 101, the image-formationoptical system 111, and the image sensor 112 a are arranged in thisorder.

The objective 101 includes: a first lens group that includes a meniscuslens component that is the closest to an image among the lens componentsof the first lens group, the meniscus lens component having a convexsurface facing the object; and a second lens group that is closer to theimage than the first lens group is. More particularly, the meniscus lenscomponent that is the closest to the image among the lens components ofthe first lens group has a lens outer diameter such that the lens outerdiameter divided by a thickness that the meniscus lens component has onan optical axis is 4 or lower. When the meniscus lens component is acemented lens, the outer diameter of the meniscus lens component refersto the outer diameter of a lens that is the closest to the image amongthe lenses that constitute the meniscus lens component. When the firstlens group includes a plurality of meniscus lens components each havinga lens outer diameter such that the lens outer diameter divided by athickness that the meniscus lens component has on the optical axis is 4or lower, the meniscus lens component that is the closest to the imageamong the lens components of the first lens group refers to the meniscuslens component that is the closest to the image among the plurality ofmeniscus lens components. A border between the first and second lensgroups may be identified in accordance with this feature.

The first lens group applies a converging effect therewithin to a pencilof diverging light rays from an object point. Subsequently, the firstlens group decreases a marginal ray height of the pencil of light rayswithin the meniscus lens component that is the closest to the imageamong the lens components of the first lens group and then emits thepencil of light rays from the concave surface of the meniscus lenscomponent toward the second lens group. In addition, the second lensgroup turns the pencil of light rays from the first lens group into apencil of parallel light rays. Accordingly, a Petzval sum can becorrected effectively, with the result that field curvatures can becorrected in a preferable manner for the entirety of a wide field ofview.

The pencil of light rays herein refers to a pencil of light rays emittedfrom one point of an object (object point). Whether a single lens or acemented lens, a lens component refers to one lens block that includeslens surfaces through which a light ray from an object point passes,wherein only a surface on an object side and a surface on an image sideamong these lens surfaces, i.e., only two of these lens surfaces, are incontact with air (or immersion liquid).

The image-formation optical system 111 has a positive refractive poweroverall and includes at least one lens component having a positiverefractive power. The objective 101 and the image-formation opticalsystem 111 form an infinity-corrected optical system such that theobjective 101 and the image-formation optical system 111 can have aspace formed therebetween through which essentially parallel lightpasses. Hence, while maintaining a preferable aberration performance, anoptical component such as an optical filter or a dichroic mirror can beinserted into an optical path between the objective 101 and theimage-formation optical system 111 on an as-needed basis.

The image sensor 112 a is a solid-state image sensor and includes aplurality of pixels. The image sensor 112 a desirably includes 4 millionor more pixels to provide an image with a high resolution.

The imaging optical system 110 satisfies the following conditionalexpression:

4×10⁶ PX _(n)1×10¹⁰  (1)

In this conditional expression, PX_(n) indicates the number of pixelsincluded in a region on the imaging plane 112 s of the image sensor 112a in which an MTF specific to an e line is 40% or higher, wherein theMTF specific to the e line is an MTF achieved at a spatial frequency of750×NA_(i) [LP/mm] and, more particularly, the lower of the MTF in asagittal direction and the MTF in a meridional direction; and NA_(i)indicates the numerical aperture of the image side of the imagingoptical system 110.

More specifically, the imaging optical system 110 desirably satisfiesconditional expression (1) when sample S is located at a position on theoptical axis on the object side of the objective 101 at which an RMSwavefront aberration is minimized when parallel light is incident on theobjective 101 from the image side and the image sensor 112 a ispositioned in a manner such that the imaging plane 112 s is situated ata position at which an MTF at a spatial frequency of 750×NA_(i) [LP/mm]is maximized.

Satisfying conditional expression (1) allows microscopic images with ahigh resolution that correspond to a wide range on sample S to becaptured.

If PX_(n) becomes lower than a lower limit of conditional expression (1)with a pixel pitch maintained such that sampling can be performed at apredetermined frequency, this will decrease an image capturing range forwhich microscopic images can be captured with a sufficient resolvingpower. To construct a virtual slide image from these images, moremicroscopic images will be necessary, and hence it will take a long timeto construct the virtual slide image. Meanwhile, if PX_(n) becomeshigher than an upper limit of conditional expression (1), the imagesensor 112 a will include excessively many pixels, and hence it willtake a long time to capture images. If PX_(n) becomes higher than theupper limit of conditional expression (1) with the size of the imagesensor maintained within a predetermined range, each single pixel willhave an excessively narrow light reception area. Hence, the imagequality will be decreased.

The imaging optical system 110 configured as described above can achievea high resolving power for a wide field of view and capture microscopicimages with a high resolution that correspond to a wide range on sampleS. In addition, the microscope system 100 can construct a high-qualityvirtual slide image in a short time by using microscopic images capturedby the imaging optical system 110.

The imaging optical system 110 desirably satisfies conditionalexpression (1-1), (1-2), or (1-3) instead of conditional expression (1).

5.2×10⁶ PX _(n)≤1×10⁹  (1-1)

7.5×10⁶ PX _(n)≤1×10⁹  (1-2)

1.1×10⁷ PX _(n)≤5×10⁸  (1-3)

The imaging optical system 110 desirably further satisfies the followingconditional expression:

400≤D/ε≤10000  (2)

In this conditional expression, D indicates a diagonal length of theimage sensor 112 a, and ε indicates an Airy disk diameter for an e lineon the imaging plane 112 s and an optical axis.

Satisfying conditional expression (2) allows microscopic images thatcorrespond to a wide range on sample S and have a high resolution to becaptured.

If D/ε is lower than a lower limit of conditional expression (2), theobjective 101 will have an excessively low numerical aperture and/or thedigital camera 112 will have an excessively narrow image-capturablerange. Hence, it will be difficult to capture microscopic images thatcorrespond to a wide range on sample S and have a high resolution. IfD/ε is higher than an upper limit of conditional expression (2), theimage-capturable range will become excessively wide relative to thenumerical aperture. This makes it difficult to maintain preferableaberration properties for a region up to the edge portions of the imagesensor.

It is desirable that the first lens group of the objective 101 include afirst lens component that is the closest to the object among the lenscomponents of the first lens group and that has a convex surface facingthe image. It is also desirable that the imaging optical system 110satisfy the following conditional expression:

1.5≤n ₁≤1.85  (3)

In this conditional expression, n₁ indicates the highest of therefractive indexes that the lenses included in the first lens componenthave for an e line.

By satisfying conditional expression (3), a spherical aberration can becorrected within the objective in a preferable manner, and afluorescence observation can be performed at a short wavelength with ahigh resolving power. An optical material that has a high refractiveindex typically features high absorption and strong autofluorescence fora short wavelength. Accordingly, a material having a refractive indexthat is not excessively high is preferably used to achieve a high SNratio in a fluorescence observation using excitation light having ashort wavelength.

When n₁ is not higher than an upper limit of conditional expression (3),a fluorescence image with a high SN ratio is obtained such that afluorescence observation and a structure analysis can be performed witha high resolving power. When n₁ is not lower than a lower limit ofconditional expression (3), divergence of light rays emitted from thefirst lens component can be limited while reducing generation ofspherical aberrations in the first lens component. This allows thespherical aberrations to be corrected in a preferable manner throughoutthe objective.

The second lens group of the objective 101 desirably includes aplurality of lens components. An objective typically largely corrects acoma aberration by means of a lens component close to an image plane. Bythe second lens group including a plurality of lens components, theintervals between these lens components can be adjusted. Hence, avariation in a coma aberration that could be caused by a manufacturingerror in, for example, the lens thickness or the radius of curvature canbe appropriately compensated for by adjusting the intervals between thelens components of the second lens group.

The objective 101 desirably includes a cemented triplet lens. Theimaging optical system 110 desirably satisfies the following conditionalexpression, where NA_(ob) indicates the numerical aperture of the objectside of the objective 101:

0.5≤NA_(ob)  (4)

An objective with a high numerical aperture that satisfies conditionalexpression (4) will have a short depth of focus. Hence, chromaticaberrations need to be corrected more accurately. By the objective 101including a cemented triplet lens, the cemented triplet lens canfunction as an achromatic lens component such that chromatic aberrationscan be corrected effectively by using the space within the objective 101effectively. Disposing the achromatic lens component within a region inwhich a high marginal ray height is provided allows the achromatic lenscomponent to achieve a sufficient function, but disposing the achromaticlens component within such a region will inevitably result in a largelens diameter. Using a cemented triplet lens as the achromatic lenscomponent allows high lens component stiffness to be maintained evenwith a large lens diameter.

The cemented triplet lens desirably consists of a negative lens and twopositive lenses having the negative lens situated therebetween. Inparticular, the cemented triplet lens desirably consists of a positivelens, a negative lens, and a positive lens, wherein an object, thepositive lens, the negative lens, and the positive lens are arranged inthis order.

The configuration of the positive-negative-positive cemented tripletlens allows the lens surfaces of the two sides of the negative lens tocorrect a chromatic aberration. Hence, the cemented triplet lens allowschromatic aberrations to be corrected more effectively.

The objective 101 may be an immersion objective that satisfiesconditional expression (5). In this case, the imaging optical system 110desirably satisfies conditional expression (6), where f_(ob) indicates afocal length that the objective 101 has for an e line, and f₁ indicatesa focal length that the first lens component has for the e line.

1≤NA_(ob)  (5)

−0.2≤f _(ob) /f ₁≤0.43  (6)

The immersion objective with a high numerical aperture that satisfiesconditional expression (5) needs to limit divergence of light rays whileconsiderably reducing generation of spherical aberrations. By satisfyingconditional expression (6), the objective 101 can correct sphericalaberrations and axial chromatic aberrations effectively while correctingthe Petzval sum in a more preferable manner.

When f_(ob)/f₁ is not lower than a lower limit of conditional expression(6), divergence of a pencil of light rays emitted from the first lenscomponent can be prevented from becoming excessively large. Hence, anaxial marginal ray height does not become excessively high within theoptical systems closer to an image than the first lens component is(hereinafter referred to as optical systems of the second lens componentand the following optical systems), so that spherical aberrations andaxial chromatic aberrations can be corrected in a preferable manner.When f_(ob)/f₁ is not higher than an upper limit of conditionalexpression (6), a difference of elevation in axial marginal ray heightcan be easily provided within the optical systems of the second lenscomponent and the following optical systems. Hence, the Petzval sum canbe corrected in a preferable manner. In particular, the lens surfacethat is the closest to the object among the lens surfaces of theimmersion objective is in contact with an immersion liquid, and hence arefractive index difference becomes small, with the result that thefirst lens component cannot remarkably correct the Petzval sum.Accordingly, it is desirable that the optical systems of the second lenscomponent and the following optical systems correct the Petzval sum.

The imaging optical system 110 desirably satisfies conditionalexpression (6-1) or (6-2) instead of conditional expression (6).

−0.1≤f _(ob) /f ₁≤0.38  (6-1)

0≤f _(ob) /f ₁≤0.34  (6-2)

The second lens group of the objective 101 desirably includes asecond-group first lens component that is the closest to the objectamong the lens components of the second lens group. The imaging opticalsystem 110 desirably satisfies the following conditional expression:

0.39≤(h ₂ −h ₁)/t ₁≤0.7  (7)

In this conditional expression, h₁ indicates the height of an axialmarginal ray at the lens surface on the object side of the second-groupfirst lens component, h₂ indicates the height of an axial marginal rayat the lens surface on the image side of the second-group first lenscomponent, and t₁ indicates a thickness that the second-group first lenscomponent has on the optical axis.

Satisfying conditional expression (7) allows coma aberrations and fieldcurvatures to be corrected within the objective in a preferable manner.More particularly, when (h₂−h₁)/t₁ is not lower than a lower limit ofconditional expression (7), the height of a marginal ray can be largelychanged within the second-group first lens component. Hence, fieldcurvatures can be sufficiently corrected, with the result that a highresolution can be maintained for a region up to edge portions. When(h₂−h₁)/t₁ is not higher than an upper limit of conditional expression(7), a light ray can be prevented from forming an excessively largerefractive angle at the object-side (incidence-side) lens surface orimage-side (emission-side) lens surface of the second-group first lenscomponent. Hence, the occurrence of high-order spherical aberrations andcoma aberrations can be reduced, with the result that a high resolutioncan be maintained for a region up to edge portions.

The imaging optical system 110 desirably satisfies conditionalexpression (7-1) instead of conditional expression (7).

0.43≤(h ₂ −h ₁)/t ₁≤0.6  (7-1)

The objective 101 may be a dry objective that satisfies conditionalexpression (8). In this case, the objective desirably includes at leastone lens component that can be moved along an optical axis.

0.85≤NA_(ob)<1  (8)

The dry objective with a high numerical aperture that satisfiesconditional expression (8) has a spherical aberration that is largelyvaried when a slight change is made in the thickness or refractive indexof cover glass. By the objective including at least one lens componentthat can be moved along the optical axis (hereinafter referred to as amovable lens component), variations in spherical aberrations can becompensated for in accordance with the movement of the movable lenscomponent.

The microscope system 100 provided with the imaging optical system 110configured as described above desirably satisfies the followingconditional expression:

3.3×10⁶ ≤PX _(i)≤1×10¹⁰  (9)

In this conditional expression, PX_(i) indicates the number of pixelsthat constitute each individual microscopic image of a plurality ofmicroscopic images captured by the imaging optical system 110 that areto be pieced together when the computer 118 constructs a virtual slideimage (hereinafter referred to as first images). When the computer 118has designated an imaging range for the digital camera 112, PX_(i)indicates a pixel count that corresponds to this imaging range. When thecomputer 118 extracts portions of a microscopic image captured by thedigital camera 112 and performs piecing process for these portions,PX_(i) indicates a pixel count that corresponds to the extractedportions of the microscopic image.

Satisfying conditional expression (9) allows a virtual slide image to beconstructed in a short time. More specifically, when PX_(i) is not lowerthan a lower limit of conditional expression (9), a wide imaging rangecan be set so that the number of images that need to be captured toconstruct a virtual slide image can be decreased, with the result thatthe virtual slide image can be constructed in a short time. When PX_(i)is not higher than an upper limit of conditional expression (9), theimage sensor 112 a do not have excessively many pixels, and hence itwill not take an excessively long time to capture a single image.

The objective may use only one of the above-described conditionalexpressions or may use a combination of conditional expressions freelyselected from these conditional expressions, and any combination can beused to achieve sufficiently advantageous effects. The upper and lowerlimits of the conditional expressions may each be independently changedto provide a new conditional expression which will also achieve similaradvantageous effects.

The following specifically describes embodiments of the imaging opticalsystem 110.

First Embodiment

FIG. 2 is a cross-sectional view of an imaging optical system 10 inaccordance with the present embodiment. FIG. 3 is a cross-sectional viewof an objective 1 in accordance with this embodiment. As depicted inFIG. 2, the imaging optical system 10 includes the objective 1, animage-formation optical system 11, and an image sensor 12 a, wherein anobject, the objective 1, the image-formation optical system 11, and theimage sensor 12 a are arranged in this order.

As depicted in FIG. 3, the objective 1 includes: a first lens group G1that includes a meniscus lens component that is the closest to an imageamong the lens components of the first lens group G1, the meniscus lenscomponent having a convex surface facing the object; and a second lensgroup G2 that is closer to the image than the first lens group G1 is.The objective 1 is a dry microscope objective.

The first lens group G1 includes a lens L1 that is a biconvex lens and acemented lens CL1, wherein the object, the lens L1, and the cementedlens CL1 are arranged in this order. The lens L1 is a first lenscomponent of the objective 1. The cemented lens CL1 is a cementeddoublet lens and consists of a lens L2 that is a biconvex lens and alens L3 that is a biconcave lens, wherein the object, the lens L2, andthe lens L3 are arranged in this order. The cemented lens CL1 is ameniscus lens component having a convex surface facing the object.

The second lens group G2 includes a cemented lens CL2, a cemented lensCL3, and a lens L8 that is a biconvex lens, wherein the object, thecemented lens CL2, the cemented lens CL3, and the lens L8 are arrangedin this order. The cemented lens CL2 is a cemented doublet lens andconsists of a lens L4 that is a biconcave lens and a lens L5 that is abiconvex lens, wherein the object, the lens L4, and the lens L5 arearranged in this order. The cemented lens CL2 is a second-group firstlens component of the objective 1. The cemented lens CL3 is a cementeddoublet lens and consists of a lens L6 that is a biconcave lens and alens L7 that is a biconvex lens, wherein the object, the lens L6, andthe lens L7 are arranged in this order.

As depicted in FIG. 2, the image-formation optical system 11 includes acemented lens CTL1 and a cemented lens CTL2, wherein the object, thecemented lens CTL1, and the cemented lens CTL2 are arranged in thisorder. The cemented lens CTL1 consists of a lens TL1 that is a biconvexlens and a lens TL2 that is a meniscus lens having a concave surfacefacing the object. The cemented lens CTL2 consists of a lens TL3 that isa biconvex lens and a lens TL4 that is a biconcave lens.

The following are various data on the imaging optical system 10, wheref_(TL) indicates the focal length of the image-formation optical system11, f_(G1) indicates a focal length that the first lens group of theobjective 1 has for an e line, f_(G2) indicates a focal length that thesecond lens group of the objective 1 has for the e line, β indicates themagnification of the imaging optical system 10, and Φ₁ indicates theouter diameter of the biconcave lens L3, i.e., the lens that is theclosest to the image among the lenses constituting the cemented lensCL1, wherein the cemented lens CL1 is the meniscus lens component thatis the closest to the image among the lens components of the first lensgroup G1.

NA_(ob)=0.160, NA_(i)=0.040, |β|=4, f_(ob)=45.000 mm, f_(TL)=180 mm,f_(G1)=21.637 mm, f_(G2)=56.531 mm, f₁=21.069 mm, n₁=1.51825, h₁=2.78mm, h₂=4.475 mm, t₁=5.5 mm, D=26 mm, ε=0.017 mm, Φ₁=9 mm,PX_(n)=7.7×10⁶, PX_(i)=7.4×10⁶

Various data on the image sensor 12 a included in the imaging opticalsystem 10 are as follows, where S_(H), S_(V), and S_(D) respectivelyindicate the long side length, short side length, and diagonal length ofthe image sensor 12 a, N_(H), N_(V), and N_(D) respectively indicate thelong side pixel count, short side pixel count, and total pixel count ofthe image sensor 12 a, and P indicates a pixel pitch.

S_(H)=20.8 mm, S_(V)=15.6 mm, S_(D)=25.6 mm, N_(H)=3200, N_(V)=2400,N_(D)=7.7×10⁶, P=6.5 μm

The following are lens data of the imaging optical system 10. INF in thelens data indicates infinity (∞).

Imaging optical system 10 s r d ne νd 0 INF 0.170 1.52626 54.41 1 INF13.244 2 20.4097 3.268 1.51825 64.14 3 −22.1977 8.021 4 9.8755 3.0901.43986 94.66 5 −10.1728 1.733 1.51825 64.14 6 7.3477 2.746 7 −5.71772.523 1.75844 52.32 8 36.266 2.977 1.43986 94.66 9 −8.5226 0.471 10−20.1257 1.561 1.48915 70.23 11 20.4365 3.897 1.43986 94.66 12 −18.18580.301 13 185.9612 3.570 1.49846 81.54 14 −14.0427 119.000 15 68.75417.732 1.48915 70.21 16 −37.5679 3.474 1.81077 40.95 17 −102.8477 0.69718 84.3099 6.024 1.83932 37.17 19 −50.71 3.030 1.64825 40.82 20 40.6619156.927 21 INF

s indicates a surface number; r, a radius of curvature (mm); d, asurface interval (mm); ne, a refractive index for an e line; νd, an Abbenumber. These marks are also applicable to the embodiments describedhereinafter. Surface numbers s0 and s1 respectively indicate an objectsurface (surface of cover glass CG on an object side) and a surface ofthe cover glass CG on an image side. Surface numbers s2 and s14respectively indicate a lens surface that is the closest to an objectamong the lens surfaces of the objective 1 and a lens surface that isthe closest to an image among the lens surfaces of the objective 1.Surface numbers s15 and s20 respectively indicate a lens surface that isthe closest to the object among the lens surfaces of the image-formationoptical system 11 and a lens surface that is the closest to the imageamong the lens surfaces of the image-formation optical system 11.Surface number s21 indicates the imaging plane of the image sensor 12 a.

As indicated in the following, the imaging optical system 10 satisfiesconditional expressions (1)-(3) and (9).

PX _(n)=7.7×10⁶  (1)

D/ε=1561  (2)

n ₁=1.51825  (3)

NA_(ob)=0.160  (4), (5), (8)

f _(ob) /f ₁=2.136  (6)

(h ₂ −h ₁)/t ₁=0.31  (7)

PX _(i)=7.4×10⁶  (9)

FIGS. 4A-4D are each an aberration diagram for the imaging opticalsystem 10 depicted in FIG. 2 and indicate aberrations that occur on theimage plane of the image sensor 12 a. FIG. 4A is a spherical aberrationdiagram. FIG. 4B illustrates a sine-condition violation amount. FIG. 4Cis an astigmatism diagram. FIG. 4D is a coma aberration diagram for aposition with an image height ratio of 0.6 (image height 7.80 mm). “M”in the figures indicates a meridional component, and “S” indicates asagittal component.

Second Embodiment

FIG. 5 is a cross-sectional view of an imaging optical system 20 inaccordance with the present embodiment. FIG. 6 is a cross-sectional viewof an objective 2 in accordance with this embodiment. As depicted inFIG. 5, the imaging optical system 20 includes the objective 2, animage-formation optical system 11, and an image sensor 12 b, wherein anobject, the objective 2, the image-formation optical system 11, and theimage sensor 12 b are arranged in this order. The image-formationoptical system 11 in the present embodiment is similar to that in thefirst embodiment.

As depicted in FIG. 6, the objective 2 includes: a first lens group G1that includes a meniscus lens component that is the closest to an imageamong the lens components of the first lens group G1, the meniscus lenscomponent having a convex surface facing the object; and a second lensgroup G2 that is closer to the image than the first lens group G1 is.The objective 2 is a dry microscope objective.

The first lens group G1 includes a lens L1 that is a meniscus lenshaving a concave surface facing the object, a lens L2 that is a meniscuslens having a concave surface facing the object, a lens L3 that is abiconvex lens, a cemented lens CL1, and a cemented lens CL2, wherein theobject, the lens L1, the lens L2, the lens L3, the cemented lens CL1,and the cemented lens CL2 are arranged in this order.

The lens L1 is a first lens component of the objective 2. The cementedlens CL1 is a cemented triplet lens and consists of a lens L4 that is abiconvex lens, a lens L5 that is a biconcave lens, and a lens L6 that isa biconvex lens, wherein the object, the lens L4, the lens L5, and thelens L6 are arranged in this order. The cemented lens CL2 is a cementeddoublet lens and consists of a lens L7 that is a biconvex lens and alens L8 that is a biconcave lens, wherein the object, the lens L7, andthe lens L8 are arranged in this order. The cemented lens CL2 is ameniscus lens component having a convex surface facing the object.

The second lens group G2 includes a lens L9 that is a meniscus lenshaving a concave surface facing the object and a lens L10 that is ameniscus lens having a concave surface facing the object, wherein theobject, the lens L9, and the lens L10 are arranged in this order. Thelens L9 is a second-group first lens component of the objective 2.

The following are various data on the imaging optical system 20, whereΦ₁ indicates the outer diameter of the biconcave lens L8, i.e., the lensthat is the closest to the image among the lenses constituting thecemented lens CL2, wherein the cemented lens CL2 is the meniscus lenscomponent that is the closest to the image among the lens components ofthe first lens group G1.

NA_(ob)=0.800, NA_(i)=0.040, |β|=20, f_(OB)=9.000 mm, f_(TL)=180 mm,f_(G1)=5.805 mm, f_(G2)=109.708 mm, f₁=36.36 mm, n₁=1.77621, h₁=4.843mm, h₂=6.193 mm, t₁=2.646 mm, D=22 mm, ε=0.017 mm, Φ₁=13 mm,PX_(n)=1.1×10⁷, PX_(i)=8.9×10⁶

Various data on the image sensor 12 b included in the imaging opticalsystem 20 are as follows.

S_(H)=17.6 mm, S_(V)=13.2 mm, S_(D)=22.0 mm, N_(H)=3910, N_(V)=2932,N_(D)=1.15×10⁷, P=4.5 μm

The following are lens data of the imaging optical system 20.

Imaging optical system 20 s r d ne νd 0 INF 0.170 1.52626 54.41 1 INF1.220 2 −4.0367 5.316 1.77621 49.6 3 −5.5638 0.278 4 −8.3753 3.9211.43986 94.66 5 −7.3726 0.296 6 30.0778 3.701 1.43986 94.66 7 −18.16882.218 8 18.2379 7.051 1.43986 94.66 9 −13.3079 1.500 1.64132 42.41 1012.5928 5.289 1.43986 94.66 11 −15.1109 0.497 12 10.8229 4.943 1.4398694.66 13 −18.5 1.500 1.64132 42.41 14 8.2723 5.000 15 −6.3912 2.6461.74435 52.64 16 −10.7265 0.731 17 −20.9997 3.049 1.74341 32.26 18−11.4968 119.000 19 68.7541 7.732 1.48915 70.21 20 −37.5679 3.4741.81077 40.95 21 −102.8477 0.697 22 84.3099 6.024 1.83932 37.17 23−50.71 3.030 1.64825 40.82 24 40.6619 156.927 25 INF

Surface numbers s0 and s1 respectively indicate an object surface(surface of cover glass CG on an object side) and a surface of the coverglass CG on an image side. Surface numbers s2 and s18 respectivelyindicate a lens surface that is the closest to an object among the lenssurfaces of the objective 2 and a lens surface that is the closest to animage among the lens surfaces of the objective 2. Surface numbers s19and s24 respectively indicate a lens surface that is the closest to theobject among the lens surfaces of the image-formation optical system 11and a lens surface that is the closest to the image among the lenssurfaces of the image-formation optical system 11. Surface number s25indicates the imaging plane of the image sensor 12 b.

As indicated in the following, the imaging optical system 20 satisfiesconditional expressions (1)-(9), excluding conditional expressions (5)and (8).

PX _(n)=1.1×10⁷  (1)

D/ε=1321  (2)

n ₁=1.77621  (3)

NA_(ob)=0.800  (4), (5), (8)

f _(ob) /f ₁=0.248  (6)

(h ₂ −h ₁)/t ₁=0.51  (7)

PX _(i)=8.9×10⁶  (9)

FIGS. 7A-7D are each an aberration diagram for the imaging opticalsystem 20 depicted in FIG. 5 and indicate aberrations that occur on theimage plane of the image sensor 12 b. FIG. 7A is a spherical aberrationdiagram. FIG. 7B illustrates a sine-condition violation amount. FIG. 7Cis an astigmatism diagram. FIG. 7D is a coma aberration diagram for aposition with an image height ratio of 0.6 (image height 6.60 mm).

Third Embodiment

FIG. 8 is a cross-sectional view of an imaging optical system 30 inaccordance with the present embodiment. FIG. 9 is a cross-sectional viewof an objective 3 in accordance with this embodiment. As depicted inFIG. 8, the imaging optical system 30 includes the objective 3, animage-formation optical system 11, and an image sensor 12 c, wherein anobject, the objective 3, the image-formation optical system 11, and theimage sensor 12 c are arranged in this order. The image-formationoptical system 11 in the present embodiment is similar to that in thefirst embodiment.

As depicted in FIG. 9, the objective 3 includes: a first lens group G1that includes a meniscus lens component that is the closest to an imageamong the lens components of the first lens group G1, the meniscus lenscomponent having a convex surface facing the object; and a second lensgroup G2 that is closer to the image than the first lens group G1 is.The objective 3 is a dry microscope objective.

The first lens group G1 includes a lens L1 that is a meniscus lenshaving a concave surface facing the object, a lens L2 that is a meniscuslens having a concave surface facing the object, a cemented lens CL1, acemented lens CL2, a cemented lens CL3, and a cemented lens CL4, whereinthe object, the lens L1, the lens L2, the cemented lens CL1, thecemented lens CL2, the cemented lens CL3, and the cemented lens CL4 arearranged in this order. The cemented lens CL1 is a movable lenscomponent that can be moved along an optical axis.

The lens L1 is a first lens component of the objective 3. The cementedlens CL1 is a cemented doublet lens and consists of a lens L3 that is abiconcave lens and a lens L4 that is a biconvex lens, wherein theobject, the lens L3, and the lens L4 are arranged in this order. Thecemented lens CL2 is a cemented doublet lens and consists of a lens L5that is a meniscus lens having a concave surface facing the image and alens L6 that is a biconvex lens, wherein the object, the lens L5, andthe lens L6 are arranged in this order. The cemented lens CL3 is acemented triplet lens and consists of a lens L7 that is a biconvex lens,a lens L8 that is a biconcave lens, and a lens L9 that is a biconvexlens, wherein the object, the lens L7, the lens L8, and the lens L9 arearranged in this order. The cemented lens CL4 is a cemented doublet lensand consists of a lens L10 that is a biconvex lens and a lens L11 thatis a biconcave lens, wherein the object, the lens L10, and the lens L11are arranged in this order. The cemented lens CL4 is a meniscus lenscomponent having a convex surface facing the object.

The second lens group G2 includes a lens L12 that is a meniscus lenshaving a concave surface facing the object and a lens L13 that is ameniscus lens having a concave surface facing the object, wherein theobject, the lens L12, and the lens L13 are arranged in this order. Thelens L12 is a second-group first lens component of the objective 3.

The following are various data on the imaging optical system 30, whereΦ₁ indicates the outer diameter of the biconcave lens L11, i.e., thelens that is the closest to the image among the lenses constituting thecemented lens CL4, wherein the cemented lens CL4 is the meniscus lenscomponent that is the closest to the image among the lens components ofthe first lens group G1.

NA_(ob)=0.945, NA_(i)=0.024, |β|=40, f_(ob)=4.500 mm, f_(TL)=180 mm,f_(G1)=2.688 mm, f_(G2)=64.133 mm, f₁=10.117 mm, n₁=1.77621, h₁=2.942mm, h₂=3.562 mm, t₁=1.541 mm, D=26 mm, s=0.028 mm, Φ₁=7 mm,PX_(n)=6.5×10⁶, PX_(i)=5.8×10⁶

Various data on the image sensor 12 c included in the imaging opticalsystem 30 are as follows.

S_(H)=20 0.8 mm, S_(V)=15.6 mm, S_(D)=26.0 mm, N_(H)=2970, N_(V)=2230,N_(D)=6.6×10⁶, P=7 μm

Lens data of the imaging optical system 30 are as follows.

Imaging optical system 30 s r d ne νd 0 INF t 1.52626 54.41 1 INF D1 2−3.0339 3.681 1.77621 49.6 3 −3.3487 0.200 4 −7.2937 2.241 1.57098 71.35 −5.5255 D5 6 −45.764 1.200 1.64132 42.41 7 12.7782 3.875 1.43986 94.668 −14.198 D8 9 71.1197 1.500 1.61664 44.49 10 15.0477 6.788 1.4398694.66 11 −10.4578 0.300 12 11.6236 6.847 1.43986 94.66 13 −10.3782 1.5501.48915 70.23 14 6.6859 4.219 1.43986 94.66 15 −32.513 0.300 16 13.94974.787 1.49846 81.54 17 −6.1667 1.000 1.88815 40.76 18 7.744 3.857 19−4.5391 1.541 1.51825 64.14 20 −9.3597 0.873 21 −12.8369 2.219 1.743432.33 22 −7.2219 119.000  23 68.7541 7.732 1.48915 70.21 24 −37.56793.474 1.81077 40.95 25 −102.8477 0.697 26 84.3099 6.024 1.83932 37.17 27−50.71 3.030 1.64825 40.82 28 40.6619 156.927  29 INF

Surface numbers s0 and s1 respectively indicate an object surface(surface of cover glass CG on an object side) and a surface of the coverglass CG on an image side. Surface numbers s2 and s22 respectivelyindicate a lens surface that is the closest to an object among the lenssurfaces of the objective 3 and a lens surface that is the closest to animage among the lens surfaces of the objective 3. Surface numbers s23and s28 respectively indicate a lens surface that is the closest to theobject among the lens surfaces of the image-formation optical system 11and a lens surface that is the closest to the image among the lenssurfaces of the image-formation optical system 11. Surface number s29indicates the imaging plane of the image sensor 12 c.

Surface interval t, i.e., the interval between the surface identified assurface number s0 and the surface identified as surface number s1,indicates the thickness of cover glass CG and is a variable amountvaried according to cover glass CG. Surface interval D1, i.e., theinterval between the surface identified as surface number s1 and thesurface identified as surface number s2, indicates an air intervalbetween cover glass CG and the objective 3 and is a variable amountvaried according to cover glass CG. Each of surface interval D5, i.e.,the interval between the surface identified as surface number s5 and thesurface identified as surface number s6, and surface interval D8, i.e.,the interval between the surface identified as surface number s8 and thesurface identified as surface number s9, indicates an airspace betweenthe movable lens component and a lens component adjacent thereto and isa variable amount varied according to the position of the movable lenscomponent. The position of the movable lens component is adjustedaccording to, for example, the thickness of cover glass CG.

Relationships between the variable amounts are as follows:

t (cover glass thickness) 0.17 0.11 0.23 D1 0.411 0.441 0.382 D5 0.7661.178 0.330 D8 0.742 0.330 1.178

As indicated in the following, the imaging optical system 30 satisfiesconditional expressions (1)-(9), excluding conditional expressions (5)and (6).

PX _(n)=6.5×10⁶  (1)

D/ε=992  (2)

n ₁=1.77621  (3)

NA_(ob)=0.945  (4), (5), (8)

f _(ob) /f ₁=0.445  (6)

(h ₂ −h ₁)/t ₁=0.40  (7)

PX _(i)=5.8×10⁶  (9)

FIGS. 10A-10D are each an aberration diagram for the imaging opticalsystem 30 depicted in FIG. 8 and indicate aberrations that occur on theimage plane of the image sensor 12 c. FIG. 10A is a spherical aberrationdiagram. FIG. 10B illustrates a sine-condition violation amount. FIG.10C is an astigmatism diagram. FIG. 10D is a coma aberration diagram fora position with an image height ratio of 0.6 (image height 7.80 mm).

Fourth Embodiment

FIG. 11 is a cross-sectional view of an imaging optical system 40 inaccordance with the present embodiment. FIG. 12 is a cross-sectionalview of an objective 4 in accordance with this embodiment. As depictedin FIG. 11, the imaging optical system 40 includes the objective 4, animage-formation optical system 11, and an image sensor 12 d, wherein anobject, the objective 4, the image-formation optical system 11, and theimage sensor 12 d are arranged in this order. The image-formationoptical system 11 in the present embodiment is similar to that in thefirst embodiment.

As depicted in FIG. 12, the objective 4 includes: a first lens group G1that includes a meniscus lens component that is the closest to an imageamong the lens components of the first lens group G1, the meniscus lenscomponent having a convex surface facing the object; and a second lensgroup G2 that is closer to the image than the first lens group G1 is.The objective 4 is an immersion microscope objective.

The first lens group G1 includes a cemented lens CL1, a lens L3 that isa meniscus lens having a concave surface facing the object, a lens L4that is a biconvex lens, a cemented lens CL2, a cemented lens CL3, alens L11 that is a meniscus lens having a concave surface facing theimage, and a cemented lens CL4, wherein the object, the cemented lensCL1, the lens L3, the lens L4, the cemented lens CL2, the cemented lensCL3, the lens L11, and the cemented lens CL4 are arranged in this order.

The cemented lens CL1 is a first lens component of the objective 4. Thecemented lens CL1 is a cemented doublet lens and consists of a lens L1that is a planoconvex lens having a plane surface facing the object anda lens L2 that is a meniscus lens having a concave surface facing theobject, wherein the object, the lens L1, and the lens L2 are arranged inthis order. The cemented lens CL2 is a cemented triplet lens andconsists of a lens L5 that is a biconvex lens, a lens L6 that is abiconcave lens, and a lens L7 that is a biconvex lens, wherein theobject, the lens L5, the lens L6, and the lens L7 are arranged in thisorder. The cemented lens CL3 is a cemented triplet lens and consists ofa lens L8 that is a meniscus lens having a concave surface facing theimage, a lens L9 that is a biconvex lens, and a lens L10 that is ameniscus lens having a concave surface facing the object, wherein theobject, the lens L8, the lens L9, and the lens L10 are arranged in thisorder. The cemented lens CL4 is a cemented doublet lens and consists ofa lens L12 that is a meniscus lens having a concave surface facing theimage and a lens L13 that is a meniscus lens having a concave surfacefacing the image, wherein the object, the lens L12, and the lens L13 arearranged in this order. The cemented lens CL4 is a meniscus lenscomponent having a convex surface facing the object.

The second lens group G2 includes a lens L14 that is a biconcave lensand a lens L15 that is a meniscus lens having a concave surface facingthe object, wherein the object, the lens L14, and the lens L15 arearranged in this order. The lens L14 is a second-group first lenscomponent of the objective 4.

The following are various data on the imaging optical system 40, whereΦ₁ indicates the outer diameter of the meniscus lens L13, i.e., the lensthat is the closest to the image among the lenses constituting thecemented lens CL4, wherein the cemented lens CL4 is the meniscus lenscomponent that is the closest to the image among the lens components ofthe first lens group G1.

NA_(ob)=1.410, NA₁=0.023, |β|=60, f_(ob)=2.999 mm, f_(TL)=180 mm,f_(G1)=2.511 mm, f_(G2)=−27.949 mm, f₁=9.544 mm, n₁=1.83945, h₁=2.409mm, h₂=2.639 mm, t₁=0.5 mm, D=22 mm, ε=0.028 mm, Φ₁=11.5 mm,PX_(n)=5.5×10⁶, PX_(i)=5.5×10⁶

Various data on the image sensor 12 d included in the imaging opticalsystem 40 are as follows.

S_(H)=20.8 mm, S_(V)=15.6 mm, S_(D)=22.0 mm, N_(H)=2708, N_(V)=2030,N_(D)=5.5×10⁶, P=6.5 μm

Lens data of the imaging optical system 40 are as follows.

Imaging optical system 40 s r d ne νd 0 INF 0.17 1.52626 54.41 1 INF0.18 1.51793 41 2 INF 0.540 1.51825 64.14 3 −1.319 5.348 1.83945 42.73 4−4.1166 0.150 5 −78.3319 1.963 1.57098 71.3 6 −14.9285 0.150 7 18.4063.895 1.43986 94.66 8 −25.3193 0.150 9 31.1937 5.046 1.43986 94.66 10−11.9163 0.500 1.64132 42.41 11 16.5897 5.162 1.43986 94.66 12 −12.85880.150 13 38.1374 0.500 1.64132 42.41 14 8.9209 7.020 1.43986 94.66 15−7.4439 0.500 1.61664 44.49 16 −71.7589 0.150 17 11.8705 2.165 1.5709871.3 18 96.6908 0.150 19 6.2225 3.339 1.57098 71.3 20 21.2446 3.0161.83945 42.73 21 3.3871 2.7792 22 −4.4975 0.5 1.77621 49.6 23 15.92152.0396 24 −160.5239 4.056 1.74341 32.26 25 −7.7872 119.000 26 68.75417.732 1.48915 70.21 27 −37.5679 3.474 1.81077 40.95 28 −102.8477 0.69729 84.3099 6.024 1.83932 37.17 30 −50.71 3.030 1.64825 40.82 31 40.6619156.927 32 INF

Surface numbers s0 and s1 respectively indicate an object surface(surface of cover glass CG on an object side) and a surface of the coverglass CG on an image side. Surface numbers s2 and s25 respectivelyindicate a lens surface that is the closest to an object among the lenssurfaces of the objective 4 and a lens surface that is the closest to animage among the lens surfaces of the objective 4. Surface numbers s26and s31 respectively indicate a lens surface that is the closest to theobject among the lens surfaces of the image-formation optical system 11and a lens surface that is the closest to the image among the lenssurfaces of the image-formation optical system 11. Surface number s32indicates the imaging plane of the image sensor 12 d.

As indicated in the following, the imaging optical system 40 satisfiesconditional expressions (1)-(9).

PX _(n)=5.5×10⁶  (1)

D/ε=776  (2)

n ₁=1.83945  (3)

NA_(ob)=1.410  (4), (5), (8)

f _(ob) /f ₁=0.314  (6)

(h ₂ −h ₁)/t ₁=0.46  (7)

PX _(i)=5.5×10⁶  (9)

FIGS. 13A-13D are each an aberration diagram for the imaging opticalsystem 40 depicted in FIG. 11 and indicate aberrations that occur on theimage plane of the image sensor 12 d. FIG. 13A is a spherical aberrationdiagram. FIG. 13B illustrates a sine-condition violation amount. FIG.13C is an astigmatism diagram. FIG. 13D is a coma aberration diagram fora position with an image height ratio of 0.6 (image height 6.60 mm).

Fifth Embodiment

FIG. 14 is a cross-sectional view of an imaging optical system 50 inaccordance with the present embodiment. FIG. 15 is a cross-sectionalview of an objective 5 in accordance with this embodiment. As depictedin FIG. 14, the imaging optical system 50 includes the objective 5, animage-formation optical system 13, and an image sensor 12 e, wherein anobject, the objective 5, the image-formation optical system 13, and theimage sensor 12 e are arranged in this order.

As depicted in FIG. 15, the objective 5 includes: a first lens group G1that includes a meniscus lens component that is the closest to an imageamong the lens components of the first lens group G1, the meniscus lenscomponent having a convex surface facing the object; and a second lensgroup G2 that is closer to the image than the first lens group G1 is.The objective 5 is an immersion microscope objective.

The first lens group G1 includes a cemented lens CL1, a lens L3 that isa biconvex lens, a lens L4 that is a biconvex lens, a cemented lens CL2,a cemented lens CL3, a cemented lens CL4, and a cemented lens CL5,wherein the object, the cemented lens CL1, the lens L3, the lens L4, thecemented lens CL2, the cemented lens CL3, the cemented lens CL4, and thecemented lens CL5 are arranged in this order.

The cemented lens CL1 is a first lens component of the objective 5. Thecemented lens CL1 is a cemented doublet lens and consists of a lens L1that is a planoconvex lens having a plane surface facing the object anda lens L2 that is a meniscus lens having a concave surface facing theobject, wherein the object, the lens L1, and the lens L2 are arranged inthis order. The cemented lens CL2 is a cemented triplet lens andconsists of a lens L5 that is a biconvex lens, a lens L6 that is abiconcave lens, and a lens L7 that is a biconvex lens, wherein theobject, the lens L5, the lens L6, and the lens L7 are arranged in thisorder. The cemented lens CL3 is a cemented triplet lens and consists ofa lens L8 that is a meniscus lens having a concave surface facing theimage, a lens L9 that is a biconvex lens, and a lens L10 that is ameniscus lens having a concave surface facing the object, wherein theobject, the lens L8, the lens L9, and the lens L10 are arranged in thisorder. The cemented lens CL4 is a cemented doublet lens and consists ofa lens L11 that is a biconvex lens and a lens L12 that is a meniscuslens having a concave surface facing the object, wherein the object, thelens L11, and the lens L12 are arranged in this order. The cemented lensCL5 is a cemented doublet lens and consists of a lens L13 that is abiconvex lens and a lens L14 that is a biconcave lens, wherein theobject, the lens L13, and the lens L14 are arranged in this order. Thecemented lens CL5 is a meniscus lens component having a convex surfacefacing the object.

The second lens group G2 includes a lens L15 that is a biconcave lensand a cemented lens CL6, wherein the object, the lens L15, and thecemented lens CL6 are arranged in this order. The lens L15 is asecond-group first lens component of the objective 5. The cemented lensCL6 is a cemented doublet lens and consists of a lens L16 that is ameniscus lens having a concave surface facing the object and a lens L17that is a meniscus lens having a concave surface facing the object,wherein the object, the lens L16, and the lens L17 are arranged in thisorder.

As depicted in FIG. 14, the image-formation optical system 13 includes acemented lens CTL1, a cemented lens CTL2, a lens TL5 that is aplanoconvex lens having a plane surface facing the image, and a lens TL6that is a meniscus lens having a concave surface facing the image,wherein the object, the cemented lens CTL1, the cemented lens CTL2, thelens TL5, and the lens TL6 are arranged in this order. The cementedlenses CTL1 and CTL2 in the present embodiment are similar to those ofthe image-formation optical system 11 in the first embodiment.

The following are various data on the imaging optical system 50, wheref_(TL) indicates the focal length of the image-formation optical system13, and 01 indicates the outer diameter of the biconcave lens L14, i.e.,the lens that is the closest to the image among the lenses constitutingthe cemented lens CL5, wherein the cemented lens CL5 is the meniscuslens component that is the closest to the image among the lenscomponents of the first lens group G1.

NA_(ob)=1.453, NA_(i)=0.019, |β|=75, f_(ob)=1.800 mm, f_(TL)=135 mm,f_(G1)=2.048 mm, f_(G2)=−12.116 mm, f₁=4.191 mm, n₁=1.80811, h₁=1.341mm, h₂=1.429 mm, t₁=1 mm, D=17.5 mm, ε=0.034 mm, Φ₁=7 mm,PX_(n)=5.9×10⁶, PX_(i)=5.9×10⁶

The following are various data on the image sensor 12 e included in theimaging optical system 50.

S_(H)=14.0 mm, S_(V)=10.5 mm, S_(D)=17.5 mm, N_(H)=2800, N_(V)=2100,N_(D)=5.9×10⁶, P=5 μm

Lens data of the imaging optical system 50 are as follows.

Imaging optical system 50 s r d ne νd 0 INF 0.17 1.52626 54.41 1 INF0.15 1.51793 41.00 2 INF 0.490 1.51825 64.14 3 −2.5256 3.245 1.8081146.53 4 −2.758 0.150 5 57.0411 2.739 1.57098 71.30 6 −15.1633 0.150 726.7162 2.064 1.43986 94.66 8 −34.6539 0.150 9 12.0693 5.530 1.4398694.66 10 −9.3615 1.300 1.64132 42.41 11 12.289 4.960 1.43986 94.66 12−10.2507 0.150 13 38.3223 1.200 1.75844 52.32 14 12.9929 4.935 1.4398694.66 15 −6.7513 1.100 1.75844 52.32 16 −13.8019 0.150 17 12.8304 3.7781.43986 94.66 18 −8.0374 1.000 1.75844 52.32 19 −28.8995 0.150 20 5.19025.3476 1.57098 71.30 21 −10.1104 1 1.64132 42.41 22 2.3315 1.7 23−3.3075 1 1.75844 52.32 24 16.1481 1.1 25 −5.4713 1 1.51825 64.14 26−22.079 4.3375 1.7434 32.33 27 −5.8878 119 28 68.7541 7.732 1.4891570.21 29 −37.5679 3.474 1.81077 40.95 30 −102.8477 0.697 31 84.30996.024 1.83932 37.17 32 −50.71 3.030 1.64825 40.82 33 40.6619 89.682 3455.4119 5.370 1.48915 70.23 35 INF 5.770 36 252.1187 3.120 1.67765 32.137 82.9177 36.659 38 INF

Surface numbers s0 and s1 respectively indicate an object surface(surface of cover glass CG on an object side) and a surface of the coverglass CG on an image side. Surface numbers s2 and s27 respectivelyindicate a lens surface that is the closest to an object among the lenssurfaces of the objective 5 and a lens surface that is the closest to animage among the lens surfaces of the objective 5. Surface numbers s28and s37 respectively indicate a lens surface that is the closest to theobject among the lens surfaces of the image-formation optical system 13and a lens surface that is the closest to the image among the lenssurfaces of the image-formation optical system 13. Surface number s38indicates the imaging plane of the image sensor 12 e.

As indicated in the following, the imaging optical system 50 satisfiesconditional expressions (1)-(9), excluding conditional expression (7).

PX _(n)=5.9×10⁶  (1)

D/ε=509  (2)

n ₁=1.80811  (3)

NA_(ob)=1.453  (4), (5), (8)

f _(ob) /f ₁=0.429  (6)

(h ₂ −h ₁)/t ₁=0.09  (7)

PX _(i)=5.9×10⁶  (9)

FIGS. 16A-16D are each an aberration diagram for the imaging opticalsystem 50 depicted in FIG. 14 and indicate aberrations that occur on theimage plane of the image sensor 12 e. FIG. 16A is a spherical aberrationdiagram. FIG. 16B illustrates a sine-condition violation amount. FIG.16C is an astigmatism diagram. FIG. 16D is a coma aberration diagram fora position with an image height ratio of 0.6 (image height 5.25 mm).

Sixth Embodiment

FIG. 17 is a cross-sectional view of an imaging optical system 60 inaccordance with the present embodiment. FIG. 18 is a cross-sectionalview of an objective 6 in accordance with this embodiment. As depictedin FIG. 17, the imaging optical system 60 includes the objective 6, animage-formation optical system 13, and an image sensor 12 f, wherein anobject, the objective 6, the image-formation optical system 13, and theimage sensor 12 f are arranged in this order. The image-formationoptical system 13 in the present embodiment is similar to that in thefifth embodiment.

As depicted in FIG. 18, the objective 6 includes: a first lens group G1that includes a meniscus lens component that is the closest to an imageamong the lens components of the first lens group G1, the meniscus lenscomponent having a convex surface facing the object; and a second lensgroup G2 that is closer to the image than the first lens group G1 is.The objective 6 is a dry microscope objective.

The first lens group G1 includes a cemented lens CL1, a lens L3 that isa biconvex lens, a lens L4 that is a biconvex lens, and a cemented lensCL2, wherein the object, the cemented lens CL1, the lens L3, the lensL4, and the cemented lens CL2 are arranged in this order.

The cemented lens CL1 is a first lens component of the objective 6. Thecemented lens CL1 is a cemented doublet lens and consists of a lens L1that is a biconcave lens and a lens L2 that is a biconvex lens, whereinthe object, the lens L1, and the lens L2 are arranged in this order. Thecemented lens CL2 is a cemented doublet lens and consists of a lens L5that is a biconvex lens and a lens L6 that is a biconcave lens, whereinthe object, the lens L5, and the lens L6 are arranged in this order. Thecemented lens CL2 is a meniscus lens component having a convex surfacefacing the object.

The second lens group G2 includes a cemented lens CL3 and a lens L9 thatis a biconvex lens, wherein the object, the cemented lens CL3, and thelens L9 are arranged in this order. The cemented lens CL3 is asecond-group first lens component of the objective 6. The cemented lensCL3 is a cemented doublet lens and consists of a lens L7 that is abiconcave lens and a lens L8 that is a biconvex lens, wherein theobject, the lens L7, and the lens L8 are arranged in this order.

The following are various data on the imaging optical system 60, whereΦ₁ indicates the outer diameter of the biconcave lens L6, i.e., the lensthat is the closest to the image among the lenses constituting thecemented lens CL2, wherein the cemented lens CL2 is the meniscus lenscomponent that is the closest to the image among the lens components ofthe first lens group G1.

NA_(ob)=0.400, NA_(i)=0.053, |β|=8, f_(ob)=18.000 mm, f_(TL)=135 mm,f_(G1)=9.911 mm, f_(G2)=88.412 mm, f₁=−51.239 mm, n₁=1.61664, h₁=3.93mm, h₂=6.448 mm, t₁=7.07 mm, D=17.5 mm, ε=0.012 mm, Φ₁=12 mm,PX_(n)=1.6×10⁷, PX_(i)=1.6×10⁷

The following are various data on the image sensor 12 f included in theimaging optical system 60.

S_(H)=14.0 mm, S_(V)=10.5 mm, S_(D)=17.5 mm, N_(H)=4668, N_(V)=3500,N_(D)=1.63×10⁷, P=3 μm

Lens data of the imaging optical system 60 are as follows.

Imaging optical system 60 s r d ne νd 0 INF 0.170 1.52626 54.41 1 INF3.712 2 −8.3986 4.221 1.61664 44.49 3 12.1766 3.480 1.49846 81.54 4−10.5755 0.200 5 125.8891 2.810 1.43986 94.66 6 −18.6353 0.201 7 14.79464.481 1.43986 94.66 8 −18.4565 1.687 9 12.8039 4.810 1.43986 94.66 10−9.1339 4.490 1.51825 64.14 11 7.2434 5.711 12 −5.268 2.900 1.5182564.14 13 70.4239 4.170 1.43986 94.66 14 −10.1954 0.226 15 199.538 3.5301.43986 94.66 16 −13.7504 119 17 68.7541 7.732 1.48915 70.21 18 −37.56793.474 1.81077 40.95 19 −102.8477 0.697 20 84.3099 6.024 1.83932 37.17 21−50.71 3.030 1.64825 40.82 22 40.6619 89.682 23 55.4119 5.370 1.4891570.23 24 INF 5.770 25 252.1187 3.120 1.67765 32.1 26 82.9177 36.659 27INF

Surface numbers s0 and s1 respectively indicate an object surface(surface of cover glass CG on an object side) and a surface of the coverglass CG on an image side. Surface numbers s2 and s16 respectivelyindicate a lens surface that is the closest to an object among the lenssurfaces of the objective 6 and a lens surface that is the closest to animage among the lens surfaces of the objective 6. Surface numbers s17and s26 respectively indicate a lens surface that is the closest to theobject among the lens surfaces of the image-formation optical system 13and a lens surface that is the closest to the image among the lenssurfaces of the image-formation optical system 13. Surface number s27indicates the imaging plane of the image sensor 12 f.

As indicated in the following, the imaging optical system 60 satisfiesconditional expressions (1)-(3) and (9).

PX _(n)=1.6×10⁷  (1)

D/ε=1401  (2)

n ₁=1.61664  (3)

NA_(ob)=0.400  (4), (5), (8)

f _(ob) /f ₁=0.351  (6)

(h ₂ −h ₁)/t ₁=0.36  (7)

PX _(i)=1.6×10⁷  (9)

FIGS. 19A-19D are each an aberration diagram for the imaging opticalsystem 60 depicted in FIG. 17 and indicate aberrations that occur on theimage plane of the image sensor 12 f. FIG. 19A is a spherical aberrationdiagram. FIG. 19B illustrates a sine-condition violation amount. FIG.19C is an astigmatism diagram. FIG. 19D is a coma aberration diagram fora position with an image height ratio of 0.6 (image height 5.25 mm).

What is claimed is:
 1. An imaging optical system comprising: anobjective; an image-formation optical system; and an image sensor,wherein an object, the objective, the image-formation optical system,and the image sensor are arranged in this order, the objective includesa first lens group that includes a meniscus lens component that isclosest to an image among lens components of the first lens group, themeniscus lens component having a convex surface facing the object, and asecond lens group that is closer to the image than the first lens groupis, the imaging optical system satisfies the following conditionalexpression:4×10⁶ PX _(n)1×10¹⁰  (1) where PX_(n) indicates a number of pixelsincluded in a region on an imaging plane of the image sensor in which anMTF specific to an e line is 40% or higher, the MTF specific to the eline is an MTF achieved at a spatial frequency of 750×NA_(i) [LP/mm],and NA_(i) indicates a numerical aperture of an image side of theimaging optical system.
 2. The imaging optical system of claim 1,satisfying the following conditional expression:400≤D/ε≤10000  (2) where D indicates a diagonal length of the imagesensor, and ε indicates an Airy disk diameter for the e line on theimaging plane and an optical axis.
 3. The imaging optical system ofclaim 1, wherein the first lens group includes a first lens componentthat is closest to the object among the lens components of the firstlens group and that has a convex surface facing the image, and theimaging optical system satisfies the following conditional expression:1.5≤n ₁≤1.85  (3) where n₁ indicates a highest of refractive indexesthat lenses included in the first lens component have for the e line. 4.The imaging optical system of claim 2, wherein the first lens groupincludes a first lens component that is closest to the object among thelens components of the first lens group and that has a convex surfacefacing the image, and the imaging optical system satisfies the followingconditional expression:1.5≤n ₁≤1.85  (3) where n₁ indicates a highest of refractive indexesthat lenses included in the first lens component have for the e line. 5.The imaging optical system of claim 1, wherein the second lens groupincludes a plurality of lens components.
 6. The imaging optical systemof claim 2, wherein the second lens group includes a plurality of lenscomponents.
 7. The imaging optical system of claim 3, wherein the secondlens group includes a plurality of lens components.
 8. The imagingoptical system of claim 4, wherein the second lens group includes aplurality of lens components.
 9. The imaging optical system of claim 1,further comprising: a cemented triplet lens, wherein the imaging opticalsystem satisfies the following conditional expression:0.5≤NA_(ob)  (4) where NA_(ob) indicates a numerical aperture of anobject side of the objective.
 10. The imaging optical system of claim 2,further comprising: a cemented triplet lens, wherein the imaging opticalsystem satisfies the following conditional expression:0.5≤NA_(ob)  (4) where NA_(ob) indicates a numerical aperture of anobject side of the objective.
 11. The imaging optical system of claim 3,further comprising: a cemented triplet lens, wherein the imaging opticalsystem satisfies the following conditional expression:0.5≤NA_(ob)  (4) where NA_(ob) indicates a numerical aperture of anobject side of the objective.
 12. The imaging optical system of claim 4,further comprising: a cemented triplet lens, wherein the imaging opticalsystem satisfies the following conditional expression:0.5≤NA_(ob)  (4) where NA_(ob) indicates a numerical aperture of anobject side of the objective.
 13. The imaging optical system of claim 5,further comprising: a cemented triplet lens, wherein the imaging opticalsystem satisfies the following conditional expression:0.5≤NA_(ob)  (4) where NA_(ob) indicates a numerical aperture of anobject side of the objective.
 14. The imaging optical system of claim 6,further comprising: a cemented triplet lens, wherein the imaging opticalsystem satisfies the following conditional expression:0.5≤NA_(ob)  (4) where NA_(ob) indicates a numerical aperture of anobject side of the objective.
 15. The imaging optical system of claim 7,further comprising: a cemented triplet lens, wherein the imaging opticalsystem satisfies the following conditional expression:0.5≤NA_(ob)  (4) where NA_(ob) indicates a numerical aperture of anobject side of the objective.
 16. The imaging optical system of claim 9,wherein the cemented triplet lens consists of a negative lens and twopositive lenses having the negative lens situated therebetween.
 17. Theimaging optical system of claim 3, wherein the objective is an immersionobjective, and the imaging optical system satisfies the followingconditional expressions:1≤NA_(ob)  (5)−0.2≤f _(ob) /f ₁≤0.43  (6) where NA_(ob) indicates a numerical apertureof an object side of the objective, f_(ob) indicates a focal length thatthe objective has for the e line, and f₁ indicates a focal length thatthe first lens component has for the e line.
 18. The imaging opticalsystem of claim 1, wherein the second lens group includes a second-groupfirst lens component that is closest to the object among lens componentsof the second lens group, and the imaging optical system satisfies thefollowing conditional expression:0.39≤(h ₂ −h ₁)/t ₁≤0.7  (7) where h₁ indicates a height of an axialmarginal ray at a lens surface on an object side of the second-groupfirst lens component, h₂ indicates a height of the axial marginal ray ata lens surface on an image side of the second-group first lenscomponent, and t₁ indicates a thickness that the second-group first lenscomponent has on an optical axis.
 19. The imaging optical system ofclaim 1, wherein the objective is a dry objective, the imaging opticalsystem further comprises at least one lens component capable of beingmoved along an optical axis, and the imaging optical system satisfiesthe following conditional expression:0.85≤NA_(ob)<1  (8) where NA_(ob) indicates a numerical aperture of anobject side of the objective.
 20. A microscope system comprising: theimaging optical system of claim 1; and an image construction unit thatconstructs a virtual slide image by piecing together a plurality offirst images captured by the imaging optical system, wherein themicroscope system satisfies the following conditional expression:3.3×10⁶ ≤PX _(i)≤1×10¹⁰  (9) where PX_(i) indicates a number of pixelsthat constitute each individual image of the plurality of first images.